The Big 4 broadcast networks announced Monday that they will begin applying the content ratings that usually appear in the upper left-hand corner of the TV screen to episodes of shows that are streamed on their websites.

ABC, CBS, Fox, NBC and Spanish-language networks Telefutura, Telemundo and Univision said they would begin using the content ratings on streaming episodes by Dec. 1. The CW, which makes episodes of its shows available on its mobile app, has yet to make a final decision on whether to put TV ratings on its streaming episodes. The CW's mobile app has been downloaded 1.1 million times.

Parents groups applauded the move. "For years, the content ratings have proven to be one of the most popular tools parents use to help make decisions about what their children watch on television," said Jim Dyke, executive director of TV Watch. "By taking this step today, these networks are giving parents an expanded set of tools to help determine what their children watch based on their own taste, style and age."

According to TV Watch, 68 percent of parents use the TV ratings system and 95 percent of those often find the ratings helpful. Some streaming services, including Hulu, already use the ratings system. And critics of it note that the content ratings are applied by the industry, not an outside or impartial party.

Network websites also will include or link to ratings system information.